import os
import cv2
import glob
import json
import tqdm
import numpy as np
from scipy.spatial.transform import Slerp, Rotation
import matplotlib.pyplot as plt 

import trimesh

import torch
import torch.nn.functional as F
from torch.utils.data import DataLoader

from .utils import get_audio_features, get_rays, get_bg_coords, convert_poses

# ref: https://github.com/NVlabs/instant-ngp/blob/b76004c8cf478880227401ae763be4c02f80b62f/include/neural-graphics-primitives/nerf_loader.h#L50
def nerf_matrix_to_ngp(pose, scale=0.33, offset=[0, 0, 0]):
    new_pose = np.array([
        [pose[1, 0], -pose[1, 1], -pose[1, 2], pose[1, 3] * scale + offset[0]],
        [pose[2, 0], -pose[2, 1], -pose[2, 2], pose[2, 3] * scale + offset[1]],
        [pose[0, 0], -pose[0, 1], -pose[0, 2], pose[0, 3] * scale + offset[2]],
        [0, 0, 0, 1],
    ], dtype=np.float32)
    return new_pose


def smooth_camera_path(poses, kernel_size=5):
    # smooth the camera trajectory...
    # poses: [N, 4, 4], numpy array

    N = poses.shape[0]
    K = kernel_size // 2
    
    trans = poses[:, :3, 3].copy() # [N, 3]
    rots = poses[:, :3, :3].copy() # [N, 3, 3]

    for i in range(N):
        start = max(0, i - K)
        end = min(N, i + K + 1)
        poses[i, :3, 3] = trans[start:end].mean(0)
        poses[i, :3, :3] = Rotation.from_matrix(rots[start:end]).mean().as_matrix()

    return poses

def polygon_area(x, y):
    x_ = x - x.mean()
    y_ = y - y.mean()
    correction = x_[-1] * y_[0] - y_[-1]* x_[0]
    main_area = np.dot(x_[:-1], y_[1:]) - np.dot(y_[:-1], x_[1:])
    return 0.5 * np.abs(main_area + correction)


def visualize_poses(poses, size=0.1):
    # poses: [B, 4, 4]

    print(f'[INFO] visualize poses: {poses.shape}')

    axes = trimesh.creation.axis(axis_length=4)
    box = trimesh.primitives.Box(extents=(2, 2, 2)).as_outline()
    box.colors = np.array([[128, 128, 128]] * len(box.entities))
    objects = [axes, box]

    for pose in poses:
        # a camera is visualized with 8 line segments.
        pos = pose[:3, 3]
        a = pos + size * pose[:3, 0] + size * pose[:3, 1] + size * pose[:3, 2]
        b = pos - size * pose[:3, 0] + size * pose[:3, 1] + size * pose[:3, 2]
        c = pos - size * pose[:3, 0] - size * pose[:3, 1] + size * pose[:3, 2]
        d = pos + size * pose[:3, 0] - size * pose[:3, 1] + size * pose[:3, 2]

        dir = (a + b + c + d) / 4 - pos
        dir = dir / (np.linalg.norm(dir) + 1e-8)
        o = pos + dir * 3

        segs = np.array([[pos, a], [pos, b], [pos, c], [pos, d], [a, b], [b, c], [c, d], [d, a], [pos, o]])
        segs = trimesh.load_path(segs)
        objects.append(segs)

    trimesh.Scene(objects).show()


class NeRFDataset_Test:
    def __init__(self, opt, device, downscale=1):
        super().__init__()
        
        self.opt = opt
        self.device = device
        self.downscale = downscale
        self.scale = opt.scale # camera radius scale to make sure camera are inside the bounding box.
        self.offset = opt.offset # camera offset
        self.bound = opt.bound # bounding box half length, also used as the radius to random sample poses.
        self.fp16 = opt.fp16

        self.start_index = opt.data_range[0]
        self.end_index = opt.data_range[1]

        self.training = False
        self.num_rays = -1
        self.preload = opt.preload # 0 = disk, 1 = cpu, 2 = gpu

        # load nerf-compatible format data.
        
        with open(opt.pose, 'r') as f:
            transform = json.load(f)

        # load image size
        self.H = int(transform['cy']) * 2 // downscale
        self.W = int(transform['cx']) * 2 // downscale
        
        # read images
        frames = transform["frames"]

        # use a slice of the dataset
        if self.end_index == -1: # abuse...
            self.end_index = len(frames)

        frames = frames[self.start_index:self.end_index]

        print(f'[INFO] load {len(frames)} frames.')

        # only load pre-calculated aud features when not live-streaming
        if not self.opt.asr:

            aud_features = np.load(self.opt.aud)

            aud_features = torch.from_numpy(aud_features)

            # support both [N, 16] labels and [N, 16, K] logits
            if len(aud_features.shape) == 3:
                aud_features = aud_features.float().permute(0, 2, 1) # [N, 16, 29] --> [N, 29, 16]    

                if self.opt.emb:
                    print(f'[INFO] argmax to aud features {aud_features.shape} for --emb mode')
                    aud_features = aud_features.argmax(1) # [N, 16]
            
            else:
                assert self.opt.emb, "aud only provide labels, must use --emb"
                aud_features = aud_features.long()

            print(f'[INFO] load {self.opt.aud} aud_features: {aud_features.shape}')

        # load action units
        import pandas as pd
        au_blink_info=pd.read_csv(self.opt.au)
        au_blink = au_blink_info[' AU45_r'].values

        self.poses = []
        self.auds = []
        self.eye_area = []
        self.torso_img = []

        for f in tqdm.tqdm(frames, desc=f'Loading data'):
            
            pose = np.array(f['transform_matrix'], dtype=np.float32) # [4, 4]
            pose = nerf_matrix_to_ngp(pose, scale=self.scale, offset=self.offset)
            self.poses.append(pose)

            # find the corresponding audio to the image frame
            if not self.opt.asr and self.opt.aud == '':
                aud = aud_features[min(f['aud_id'], aud_features.shape[0] - 1)] # careful for the last frame...
                self.auds.append(aud)

            if self.opt.exp_eye:
                
                # if 'eye_ratio' in f:
                #     area = f['eye_ratio']
                # else:
                #     area = 0.25 # default value for opened eye
                # action units blink AU45
                area = au_blink[f['img_id']]
                area = np.clip(area, 0, 2) / 2
                # area = area + np.random.rand() / 10
                
                self.eye_area.append(area)
            
            # load frame-wise bg
        
            if self.opt.torso_imgs!='':
                torso_img_path = os.path.join(self.opt.torso_imgs, str(f['img_id']) + '.png')

                if self.preload > 0:
                    torso_img = cv2.imread(torso_img_path, cv2.IMREAD_UNCHANGED) # [H, W, 4]
                    torso_img = cv2.cvtColor(torso_img, cv2.COLOR_BGRA2RGBA)
                    torso_img = torso_img.astype(np.float32) / 255 # [H, W, 3/4]

                    self.torso_img.append(torso_img)
                else:
                    self.torso_img.append(torso_img_path)
        
        if self.opt.torso_imgs!='':
            if self.preload > 0:
                self.torso_img = torch.from_numpy(np.stack(self.torso_img, axis=0)) # [N, H, W, C]
            else:
                self.torso_img = np.array(self.torso_img)
            if self.preload > 1:  #gpu
                self.torso_img = self.torso_img.to(torch.half).to(self.device)
            
        
        # load pre-extracted background image (should be the same size as training image...)

        if self.opt.bg_img == 'white': # special
            bg_img = np.ones((self.H, self.W, 3), dtype=np.float32)
        elif self.opt.bg_img == 'black': # special
            bg_img = np.zeros((self.H, self.W, 3), dtype=np.float32)
        else: # load from file
            bg_img = cv2.imread(self.opt.bg_img, cv2.IMREAD_UNCHANGED) # [H, W, 3]
            if bg_img.shape[0] != self.H or bg_img.shape[1] != self.W:
                bg_img = cv2.resize(bg_img, (self.W, self.H), interpolation=cv2.INTER_AREA)
            bg_img = cv2.cvtColor(bg_img, cv2.COLOR_BGR2RGB)
            bg_img = bg_img.astype(np.float32) / 255 # [H, W, 3/4]

        self.bg_img = bg_img

        self.poses = np.stack(self.poses, axis=0)

        # smooth camera path...
        if self.opt.smooth_path:
            self.poses = smooth_camera_path(self.poses, self.opt.smooth_path_window)
            
        self.poses = torch.from_numpy(self.poses) # [N, 4, 4]
        
        if self.opt.asr:
            # live streaming, no pre-calculated auds
            self.auds = None
        else:
            # auds corresponding to images
            if self.opt.aud == '':
                self.auds = torch.stack(self.auds, dim=0) # [N, 32, 16]
            # auds is novel, may have a different length with images
            else:
                self.auds = aud_features
        
        self.bg_img = torch.from_numpy(self.bg_img)

        if self.preload > 1 or self.opt.torso_imgs=='':  #gpu
            self.bg_img = self.bg_img.to(torch.half).to(self.device)

        if self.opt.exp_eye:
            self.eye_area = np.array(self.eye_area, dtype=np.float32) # [N]
            print(f'[INFO] eye_area: {self.eye_area.min()} - {self.eye_area.max()}')

            if self.opt.smooth_eye:

                # naive 5 window average
                ori_eye = self.eye_area.copy()
                for i in range(ori_eye.shape[0]):
                    start = max(0, i - 1)
                    end = min(ori_eye.shape[0], i + 2)
                    self.eye_area[i] = ori_eye[start:end].mean()

            self.eye_area = torch.from_numpy(self.eye_area).view(-1, 1) # [N, 1]

        # always preload
        self.poses = self.poses.to(self.device)

        if self.auds is not None:
            self.auds = self.auds.to(self.device)
        
        if self.opt.exp_eye:
            self.eye_area = self.eye_area.to(self.device)

        # load intrinsics
        
        fl_x = fl_y = transform['focal_len']

        cx = (transform['cx'] / downscale)
        cy = (transform['cy'] / downscale)

        self.intrinsics = np.array([fl_x, fl_y, cx, cy])

        # directly build the coordinate meshgrid in [-1, 1]^2
        self.bg_coords = get_bg_coords(self.H, self.W, self.device) # [1, H*W, 2] in [-1, 1]
    
    def mirror_index(self, index):
        size = self.poses.shape[0]
        turn = index // size
        res = index % size
        if turn % 2 == 0:
            return res
        else:
            return size - res - 1

    def collate(self, index):

        B = len(index) # a list of length 1
        # assert B == 1

        results = {}

        # audio use the original index
        if self.auds is not None:
            auds = get_audio_features(self.auds, self.opt.att, index[0]).to(self.device)
            results['auds'] = auds

        # head pose and bg image may mirror (replay --> <-- --> <--).
        index[0] = self.mirror_index(index[0])

        poses = self.poses[index].to(self.device) # [B, 4, 4]
        
        rays = get_rays(poses, self.intrinsics, self.H, self.W, self.num_rays, self.opt.patch_size)

        results['index'] = index # for ind. code
        results['H'] = self.H
        results['W'] = self.W
        results['rays_o'] = rays['rays_o']
        results['rays_d'] = rays['rays_d']

        if self.opt.exp_eye:
            results['eye'] = self.eye_area[index].to(self.device) # [1]
        else:
            results['eye'] = None
        
        # load bg
        if self.opt.torso_imgs!='':
            bg_torso_img = self.torso_img[index]
            if self.preload == 0: # on the fly loading
                bg_torso_img = cv2.imread(bg_torso_img[0], cv2.IMREAD_UNCHANGED) # [H, W, 4]
                bg_torso_img = cv2.cvtColor(bg_torso_img, cv2.COLOR_BGRA2RGBA)
                bg_torso_img = bg_torso_img.astype(np.float32) / 255 # [H, W, 3/4]
                bg_torso_img = torch.from_numpy(bg_torso_img).unsqueeze(0)
            bg_torso_img = bg_torso_img[..., :3] * bg_torso_img[..., 3:] + self.bg_img * (1 - bg_torso_img[..., 3:])
            bg_torso_img = bg_torso_img.view(B, -1, 3).to(self.device)
            if not self.opt.torso:
                bg_img = bg_torso_img
            else:
                bg_img = self.bg_img.view(1, -1, 3).repeat(B, 1, 1).to(self.device)
        else:
            bg_img = self.bg_img.view(1, -1, 3).repeat(B, 1, 1).to(self.device)

        results['bg_color'] = bg_img

        bg_coords = self.bg_coords # [1, N, 2]
        results['bg_coords'] = bg_coords

        # results['poses'] = convert_poses(poses) # [B, 6]
        # results['poses_matrix'] = poses # [B, 4, 4]
        results['poses'] = poses # [B, 4, 4]

        return results

    def dataloader(self):

    
        # test with novel auds, then use its length
        if self.auds is not None:
            size = self.auds.shape[0]
        # live stream test, use 2 * len(poses), so it naturally mirrors.
        else:
            size = 2 * self.poses.shape[0]

        loader = DataLoader(list(range(size)), batch_size=1, collate_fn=self.collate, shuffle=False, num_workers=0)
        loader._data = self # an ugly fix... we need poses in trainer.

        # do evaluate if has gt images and use self-driven setting
        loader.has_gt = False

        return loader


class NeRFDataset:
    def __init__(self, opt, device, type='train', downscale=1):
        super().__init__()
        
        self.opt = opt
        self.device = device
        self.type = type # train, val, test
        self.downscale = downscale
        self.root_path = opt.path
        self.preload = opt.preload # 0 = disk, 1 = cpu, 2 = gpu
        self.scale = opt.scale # camera radius scale to make sure camera are inside the bounding box.
        self.offset = opt.offset # camera offset
        self.bound = opt.bound # bounding box half length, also used as the radius to random sample poses.
        self.fp16 = opt.fp16

        self.start_index = opt.data_range[0]
        self.end_index = opt.data_range[1]

        self.training = self.type in ['train', 'all', 'trainval']
        self.num_rays = self.opt.num_rays if self.training else -1

        # load nerf-compatible format data.
      
         # load all splits (train/valid/test)
        if type == 'all':
            transform_paths = glob.glob(os.path.join(self.root_path, '*.json'))
            transform = None
            for transform_path in transform_paths:
                with open(transform_path, 'r') as f:
                    tmp_transform = json.load(f)
                    if transform is None:
                        transform = tmp_transform
                    else:
                        transform['frames'].extend(tmp_transform['frames'])
        # load train and val split
        elif type == 'trainval':
            with open(os.path.join(self.root_path, f'transforms_train.json'), 'r') as f:
                transform = json.load(f)
            with open(os.path.join(self.root_path, f'transforms_val.json'), 'r') as f:
                transform_val = json.load(f)
            transform['frames'].extend(transform_val['frames'])
        # only load one specified split
        else:
            # no test, use val as test
            _split = 'val' if type == 'test' else type
            with open(os.path.join(self.root_path, f'transforms_{_split}.json'), 'r') as f:
                transform = json.load(f)

        # load image size
        if 'h' in transform and 'w' in transform:
            self.H = int(transform['h']) // downscale
            self.W = int(transform['w']) // downscale
        else:
            self.H = int(transform['cy']) * 2 // downscale
            self.W = int(transform['cx']) * 2 // downscale
        
        # read images
        frames = transform["frames"]

        # use a slice of the dataset
        if self.end_index == -1: # abuse...
            self.end_index = len(frames)

        frames = frames[self.start_index:self.end_index]
        print(f'[INFO] load {len(frames)} {type} frames.')

        # only load pre-calculated aud features when not live-streaming
        if not self.opt.asr:

            # empty means the default self-driven extracted features.
            if self.opt.aud == '':
                if 'esperanto' in self.opt.asr_model:
                    aud_features = np.load(os.path.join(self.root_path, 'aud_eo.npy'))
                elif 'deepspeech' in self.opt.asr_model:
                    aud_features = np.load(os.path.join(self.root_path, 'aud_ds.npy'))
                # elif 'hubert_cn' in self.opt.asr_model:
                #     aud_features = np.load(os.path.join(self.root_path, 'aud_hu_cn.npy'))
                elif 'hubert' in self.opt.asr_model:
                    aud_features = np.load(os.path.join(self.root_path, 'aud_hu.npy'))
                else:
                    aud_features = np.load(os.path.join(self.root_path, 'aud.npy'))
            # cross-driven extracted features. 
            else:
                aud_features = np.load(self.opt.aud)

            aud_features = torch.from_numpy(aud_features)

            # support both [N, 16] labels and [N, 16, K] logits
            if len(aud_features.shape) == 3:
                aud_features = aud_features.float().permute(0, 2, 1) # [N, 16, 29] --> [N, 29, 16]    

                if self.opt.emb:
                    print(f'[INFO] argmax to aud features {aud_features.shape} for --emb mode')
                    aud_features = aud_features.argmax(1) # [N, 16]
            
            else:
                assert self.opt.emb, "aud only provide labels, must use --emb"
                aud_features = aud_features.long()

            print(f'[INFO] load {self.opt.aud} aud_features: {aud_features.shape}')

        # load action units
        import pandas as pd
        au_blink_info=pd.read_csv(os.path.join(self.root_path, 'au.csv'))
        au_blink = au_blink_info[' AU45_r'].values

        self.torso_img = []
        self.images = []

        self.poses = []
        self.exps = []

        self.auds = []
        self.face_rect = []
        self.lhalf_rect = []
        self.lips_rect = []
        self.eye_area = []
        self.eye_rect = []

        for f in tqdm.tqdm(frames, desc=f'Loading {type} data'):

            f_path = os.path.join(self.root_path, 'gt_imgs', str(f['img_id']) + '.jpg')

            if not os.path.exists(f_path):
                print('[WARN]', f_path, 'NOT FOUND!')
                continue
            
            pose = np.array(f['transform_matrix'], dtype=np.float32) # [4, 4]
            pose = nerf_matrix_to_ngp(pose, scale=self.scale, offset=self.offset)
            self.poses.append(pose)

            if self.preload > 0:
                image = cv2.imread(f_path, cv2.IMREAD_UNCHANGED) # [H, W, 3] o [H, W, 4]
                image = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
                image = image.astype(np.float32) / 255 # [H, W, 3/4]

                self.images.append(image)
            else:
                self.images.append(f_path)

            # load frame-wise bg
        
            torso_img_path = os.path.join(self.root_path, 'torso_imgs', str(f['img_id']) + '.png')

            if self.preload > 0:
                torso_img = cv2.imread(torso_img_path, cv2.IMREAD_UNCHANGED) # [H, W, 4]
                torso_img = cv2.cvtColor(torso_img, cv2.COLOR_BGRA2RGBA)
                torso_img = torso_img.astype(np.float32) / 255 # [H, W, 3/4]

                self.torso_img.append(torso_img)
            else:
                self.torso_img.append(torso_img_path)

            # find the corresponding audio to the image frame
            if not self.opt.asr and self.opt.aud == '':
                aud = aud_features[min(f['aud_id'], aud_features.shape[0] - 1)] # careful for the last frame...
                self.auds.append(aud)

            # load lms and extract face
            lms = np.loadtxt(os.path.join(self.root_path, 'ori_imgs', str(f['img_id']) + '.lms')) # [68, 2]

            lh_xmin, lh_xmax = int(lms[31:36, 1].min()), int(lms[:, 1].max()) # actually lower half area
            xmin, xmax = int(lms[:, 1].min()), int(lms[:, 1].max())
            ymin, ymax = int(lms[:, 0].min()), int(lms[:, 0].max())
            self.face_rect.append([xmin, xmax, ymin, ymax])
            self.lhalf_rect.append([lh_xmin, lh_xmax, ymin, ymax])

            if self.opt.exp_eye:
                # eyes_left = slice(36, 42)
                # eyes_right = slice(42, 48)

                # area_left = polygon_area(lms[eyes_left, 0], lms[eyes_left, 1])
                # area_right = polygon_area(lms[eyes_right, 0], lms[eyes_right, 1])

                # # area percentage of two eyes of the whole image...
                # area = (area_left + area_right) / (self.H * self.W) * 100

                # action units blink AU45
                area = au_blink[f['img_id']]
                area = np.clip(area, 0, 2) / 2
                # area = area + np.random.rand() / 10
                self.eye_area.append(area)

                xmin, xmax = int(lms[36:48, 1].min()), int(lms[36:48, 1].max())
                ymin, ymax = int(lms[36:48, 0].min()), int(lms[36:48, 0].max())
                self.eye_rect.append([xmin, xmax, ymin, ymax])

            if self.opt.finetune_lips:
                lips = slice(48, 60)
                xmin, xmax = int(lms[lips, 1].min()), int(lms[lips, 1].max())
                ymin, ymax = int(lms[lips, 0].min()), int(lms[lips, 0].max())

                # padding to H == W
                cx = (xmin + xmax) // 2
                cy = (ymin + ymax) // 2

                l = max(xmax - xmin, ymax - ymin) // 2
                xmin = max(0, cx - l)
                xmax = min(self.H, cx + l)
                ymin = max(0, cy - l)
                ymax = min(self.W, cy + l)

                self.lips_rect.append([xmin, xmax, ymin, ymax])
        
        # load pre-extracted background image (should be the same size as training image...)

        if self.opt.bg_img == 'white': # special
            bg_img = np.ones((self.H, self.W, 3), dtype=np.float32)
        elif self.opt.bg_img == 'black': # special
            bg_img = np.zeros((self.H, self.W, 3), dtype=np.float32)
        else: # load from file
            # default bg
            if self.opt.bg_img == '':
                self.opt.bg_img = os.path.join(self.root_path, 'bc.jpg')
            bg_img = cv2.imread(self.opt.bg_img, cv2.IMREAD_UNCHANGED) # [H, W, 3]
            if bg_img.shape[0] != self.H or bg_img.shape[1] != self.W:
                bg_img = cv2.resize(bg_img, (self.W, self.H), interpolation=cv2.INTER_AREA)
            bg_img = cv2.cvtColor(bg_img, cv2.COLOR_BGR2RGB)
            bg_img = bg_img.astype(np.float32) / 255 # [H, W, 3/4]

        self.bg_img = bg_img

        self.poses = np.stack(self.poses, axis=0)

        # smooth camera path...
        if self.opt.smooth_path:
            self.poses = smooth_camera_path(self.poses, self.opt.smooth_path_window)
            
        self.poses = torch.from_numpy(self.poses) # [N, 4, 4]

        if self.preload > 0:
            self.images = torch.from_numpy(np.stack(self.images, axis=0)) # [N, H, W, C]
            self.torso_img = torch.from_numpy(np.stack(self.torso_img, axis=0)) # [N, H, W, C]
        else:
            self.images = np.array(self.images)
            self.torso_img = np.array(self.torso_img)

        if self.opt.asr:
            # live streaming, no pre-calculated auds
            self.auds = None
        else:
            # auds corresponding to images
            if self.opt.aud == '':
                self.auds = torch.stack(self.auds, dim=0) # [N, 32, 16]
            # auds is novel, may have a different length with images
            else:
                self.auds = aud_features
        
        self.bg_img = torch.from_numpy(self.bg_img)

        if self.opt.exp_eye:
            self.eye_area = np.array(self.eye_area, dtype=np.float32) # [N]
            print(f'[INFO] eye_area: {self.eye_area.min()} - {self.eye_area.max()}')

            if self.opt.smooth_eye:

                # naive 5 window average
                ori_eye = self.eye_area.copy()
                for i in range(ori_eye.shape[0]):
                    start = max(0, i - 1)
                    end = min(ori_eye.shape[0], i + 2)
                    self.eye_area[i] = ori_eye[start:end].mean()

            self.eye_area = torch.from_numpy(self.eye_area).view(-1, 1) # [N, 1]

        
        # calculate mean radius of all camera poses
        self.radius = self.poses[:, :3, 3].norm(dim=-1).mean(0).item()
        #print(f'[INFO] dataset camera poses: radius = {self.radius:.4f}, bound = {self.bound}')

        
        # [debug] uncomment to view all training poses.
        # visualize_poses(self.poses.numpy())

        # [debug] uncomment to view examples of randomly generated poses.
        # visualize_poses(rand_poses(100, self.device, radius=self.radius).cpu().numpy())

        if self.preload > 1:
            self.poses = self.poses.to(self.device)

            if self.auds is not None:
                self.auds = self.auds.to(self.device)

            self.bg_img = self.bg_img.to(torch.half).to(self.device)

            self.torso_img = self.torso_img.to(torch.half).to(self.device)
            self.images = self.images.to(torch.half).to(self.device)
            
            if self.opt.exp_eye:
                self.eye_area = self.eye_area.to(self.device)

        # load intrinsics
        if 'focal_len' in transform:
            fl_x = fl_y = transform['focal_len']
        elif 'fl_x' in transform or 'fl_y' in transform:
            fl_x = (transform['fl_x'] if 'fl_x' in transform else transform['fl_y']) / downscale
            fl_y = (transform['fl_y'] if 'fl_y' in transform else transform['fl_x']) / downscale
        elif 'camera_angle_x' in transform or 'camera_angle_y' in transform:
            # blender, assert in radians. already downscaled since we use H/W
            fl_x = self.W / (2 * np.tan(transform['camera_angle_x'] / 2)) if 'camera_angle_x' in transform else None
            fl_y = self.H / (2 * np.tan(transform['camera_angle_y'] / 2)) if 'camera_angle_y' in transform else None
            if fl_x is None: fl_x = fl_y
            if fl_y is None: fl_y = fl_x
        else:
            raise RuntimeError('Failed to load focal length, please check the transforms.json!')

        cx = (transform['cx'] / downscale) if 'cx' in transform else (self.W / 2)
        cy = (transform['cy'] / downscale) if 'cy' in transform else (self.H / 2)
    
        self.intrinsics = np.array([fl_x, fl_y, cx, cy])

        # directly build the coordinate meshgrid in [-1, 1]^2
        self.bg_coords = get_bg_coords(self.H, self.W, self.device) # [1, H*W, 2] in [-1, 1]


    def mirror_index(self, index):
        size = self.poses.shape[0]
        turn = index // size
        res = index % size
        if turn % 2 == 0:
            return res
        else:
            return size - res - 1


    def collate(self, index):

        B = len(index) # a list of length 1
        # assert B == 1

        results = {}

        # audio use the original index
        if self.auds is not None:
            auds = get_audio_features(self.auds, self.opt.att, index[0]).to(self.device)
            results['auds'] = auds

        # head pose and bg image may mirror (replay --> <-- --> <--).
        index[0] = self.mirror_index(index[0])

        poses = self.poses[index].to(self.device) # [B, 4, 4]
        
        if self.training and self.opt.finetune_lips:
            rect = self.lips_rect[index[0]]
            results['rect'] = rect
            rays = get_rays(poses, self.intrinsics, self.H, self.W, -1, rect=rect)
        else:
            rays = get_rays(poses, self.intrinsics, self.H, self.W, self.num_rays, self.opt.patch_size)

        results['index'] = index # for ind. code
        results['H'] = self.H
        results['W'] = self.W
        results['rays_o'] = rays['rays_o']
        results['rays_d'] = rays['rays_d']

        # get a mask for rays inside rect_face
        if self.training:
            xmin, xmax, ymin, ymax = self.face_rect[index[0]]
            face_mask = (rays['j'] >= xmin) & (rays['j'] < xmax) & (rays['i'] >= ymin) & (rays['i'] < ymax) # [B, N]
            results['face_mask'] = face_mask
            
            xmin, xmax, ymin, ymax = self.lhalf_rect[index[0]]
            lhalf_mask = (rays['j'] >= xmin) & (rays['j'] < xmax) & (rays['i'] >= ymin) & (rays['i'] < ymax) # [B, N]
            results['lhalf_mask'] = lhalf_mask

        if self.opt.exp_eye:
            results['eye'] = self.eye_area[index].to(self.device) # [1]
            if self.training:
                results['eye'] += (np.random.rand()-0.5) / 10
                xmin, xmax, ymin, ymax = self.eye_rect[index[0]]
                eye_mask = (rays['j'] >= xmin) & (rays['j'] < xmax) & (rays['i'] >= ymin) & (rays['i'] < ymax) # [B, N]
                results['eye_mask'] = eye_mask

        else:
            results['eye'] = None

        # load bg
        bg_torso_img = self.torso_img[index]
        if self.preload == 0: # on the fly loading
            bg_torso_img = cv2.imread(bg_torso_img[0], cv2.IMREAD_UNCHANGED) # [H, W, 4]
            bg_torso_img = cv2.cvtColor(bg_torso_img, cv2.COLOR_BGRA2RGBA)
            bg_torso_img = bg_torso_img.astype(np.float32) / 255 # [H, W, 3/4]
            bg_torso_img = torch.from_numpy(bg_torso_img).unsqueeze(0)
        bg_torso_img = bg_torso_img[..., :3] * bg_torso_img[..., 3:] + self.bg_img * (1 - bg_torso_img[..., 3:])
        bg_torso_img = bg_torso_img.view(B, -1, 3).to(self.device)

        if not self.opt.torso:
            bg_img = bg_torso_img
        else:
            bg_img = self.bg_img.view(1, -1, 3).repeat(B, 1, 1).to(self.device)

        if self.training:
            bg_img = torch.gather(bg_img, 1, torch.stack(3 * [rays['inds']], -1)) # [B, N, 3]

        results['bg_color'] = bg_img

        if self.opt.torso and self.training:
            bg_torso_img = torch.gather(bg_torso_img, 1, torch.stack(3 * [rays['inds']], -1)) # [B, N, 3]
            results['bg_torso_color'] = bg_torso_img

        images = self.images[index] # [B, H, W, 3/4]
        if self.preload == 0:
            images = cv2.imread(images[0], cv2.IMREAD_UNCHANGED) # [H, W, 3]
            images = cv2.cvtColor(images, cv2.COLOR_BGR2RGB)
            images = images.astype(np.float32) / 255 # [H, W, 3]
            images = torch.from_numpy(images).unsqueeze(0)
        images = images.to(self.device)

        if self.training:
            C = images.shape[-1]
            images = torch.gather(images.view(B, -1, C), 1, torch.stack(C * [rays['inds']], -1)) # [B, N, 3/4]
            
        results['images'] = images

        if self.training:
            bg_coords = torch.gather(self.bg_coords, 1, torch.stack(2 * [rays['inds']], -1)) # [1, N, 2]
        else:
            bg_coords = self.bg_coords # [1, N, 2]

        results['bg_coords'] = bg_coords

        # results['poses'] = convert_poses(poses) # [B, 6]
        # results['poses_matrix'] = poses # [B, 4, 4]
        results['poses'] = poses # [B, 4, 4]
            
        return results

    def dataloader(self):

        if self.training:
            # training len(poses) == len(auds)
            size = self.poses.shape[0]
        else:
            # test with novel auds, then use its length
            if self.auds is not None:
                size = self.auds.shape[0]
            # live stream test, use 2 * len(poses), so it naturally mirrors.
            else:
                size = 2 * self.poses.shape[0]

        loader = DataLoader(list(range(size)), batch_size=1, collate_fn=self.collate, shuffle=self.training, num_workers=0)
        loader._data = self # an ugly fix... we need poses in trainer.

        # do evaluate if has gt images and use self-driven setting
        loader.has_gt = (self.opt.aud == '')

        return loader